Moisture-proof accessible brush holder



April 1969 R. T. WALTER 3,436,578

MOISTURE-PROOF ACCESSIBLE BRUSH HOLDER Filed April '24, 1968 FIG.

FIG. 3 r'lllll" 55 4 5-, all]! is INVENTOR RICHARD T. WALTER ATTORNEY United States Patent O US. Cl. 310-247 13 Claims ABSTRACT OF THE DISCLOSURE The device disclosed herein is a shunt-type brush holder assembly for an electric motor and includes a hollow, elongated, insulating body having an insulating plug threaded in one end thereof and which is accessible externally of the motor. A conductive sleeve is positioned within the body and is electrically connected to a connector slidable therein by a brush cap and a conventional pigtail. The brush is normally biased outwardly of the sleeve by a spring trapped between the brush and the cap while the plug and the cap cooperatively engage in assembly causing the plug to sealingly engage the body thereby preventing moisture from gaining access to the live metal parts.

SUMMARY OF THE INVENTION The present invention deals specifically with the interfitting construction of an insulating brush holder body and plug in an externally accessible, shunt-type brush holder assembly which seals the internal, live metal parts from external moisture. The plug is adapted to be detachably fixed (threaded) to the body and has a deflectable, substantially continuous peripheral part adapted to engage a substantially continuous surface on the body. As the plug is assembled to the body, as by threading therein, stationary means therein engages and presses the deflectable part into tight, sealing engagement with the body surface.

Main objects of the present invention, therefore, are to provide an improved, shunt-type, externally accessible brush holder assembly which prevents external moisture from gaining access to the live metal parts and creating a shock hazard, and achieves this by cooperative engagement of the basic brush assembly components.

Further important objects of this invention are to provide an improved brush holder assembly of the above character which retains its effectiveness even after repeated use and which permits service and inspection of the brushes without requiring special tools.

Additional objects are to provide an improved brush holder assembly of the above character which is relatively inexpensive to manufacture, rugged in construction and reliable in use.

Other objects and advantages of the invention will become more apparent from a consideration of the detailed description to follow taken together with the drawings annexed hereto.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view illustrating a portable electric power tool with which the present invention finds use;

FIG. 2 is an enlarged sectional view of FIG. 1 taken along the line 2-2 thereof;

FIG. 3 is an enlarged view of a portion of FIG. 2 and showing the parts before full assembly; and

FIG. 4 is a view, similar to FIG. 3, but showing the parts after full assembly and with the moisture seal formed.

BROAD STATEMENT OF THE INVENTION Broadly described, the present invention relates to a moisture-proof brush holder assembly comprising a housing, an insulated brush holder body mounted in the housing, a conductive sleeve within the body, a brush guided for longitudinal sliding movement within the sleeve, a connector cap having an annular peripheral flange at least a portion of which is seated on said sleeve, a spring between the cap and the brush constantly urging the brush out of the sleeve, the annular peripheral flange on the cap being provided with a conically-tapered surface which converges in a direction away from the direction of brush travel, and an insulated plug threadably engaged with the insulated brush holder body, said plug having an innermost undercut annular portion provided with a conically-tapered surface engaging the respective conical surface of said cap, whereby said annular portion of said plug is cammed radially outwardly into sealing engagement with said body as said plug is tightened therewithin, thereby providing a seal which prevents moisture from entering the brush holder assembly and otherwise creating a shock hazard.

In another aspect, the present invention relates to an electric motor device of the type having a housing with an electric motor supported therein, and includes a moistureproof brush holder assembly accessible externally of the housing and comprising an insulating body having a pair of ends, brush means having a portion extending through one end of the holder internally of the housing, plug means threadedly connected to the other end of the holder and accessible externally of the housing, stationary means within said body, said plug means having a continuous, deflectable portion engageable with said stationary means and cooperable with a complementary continuous surface on said body, whereby said continuous portion is deflected by said stationary means into tight sealing engagement with said body surface when said plug means is connected to said body.

In still another aspect, the present invention includes a brush holder assembly for use with an electric motor device, said assembly comprising an elongated body, having an opening therethrough, a substantially continuous annular surface in said body, a carbon brush slidably disposed in said body, spring means within said body he hind said brush and normally biasing said brush outwardly of one end of said body, stationary cam means in said body, a plug threadedly received in the other end of said body and having a substantially continuous, deflectable, annular portion adjacent the inner end of said plug, said annular portion engaging said cam means whereby to deflect said annular portion into tight sealing engagement with said body surface when said plug is threaded into said body.

DETAILED DESCRIPTION Referring now more specifically to the drawings, an electric drill, which is one type of device in which the present invention finds use, is illustrated generally at 11 in FIG. 1 and is seen to include a housing 13 having a gear case 15 secured thereto. An electric motor 18 is supported within the housing 13 and drives a spindle (not shown) keyed to a chuck 17. The motor 18 is powered from an electrical source connected thereto by a line cord 19. The housing 13 has a handle 21 rigid therewith in which is mounted a trigger switch 23 for convenient on-oif control of the motor 18.

As seen in FIG. 2, electric current is supplied to the motor 18 through a pair of carbon brushes 25 (only one of which is shown) which engage a rotatable commutator 27 forming part of the motor 18. Each of the brushes 25 is carried by a novel brush holder assembly 29 supported upon the motor housing 13 at diametrically opposed positions relative to the commutator 27. The brush holder assemblies 29 are substantially identical so that a description of one will suflice here.

Thus, as shown in FIG. 2, the brush holder assembly 29 includes a hollow elongated body 31 constructed from a suitable electrical insulating material and secured within an opening 32 in the housing 13 by a pin 34. The body 31 has a passage 33 therethrough from end-to-end. An electrically conductive, sleeve insert 35 is fitted within the passage 33 and has a radial shoulder 37 seated against a shoulder 39 in the body 31. The sleeve 35, preferably constructed of brass, has its inner end projecting beyond the inner end of the body 31 and is adapted to have an electrical lead 39 connected thereto through a garter spring 41.

The sleeve 35 guidably and slidably receives the brush and has a compression spring 43 disposed therein behind the brush 25. The spring 43 is backed by a conductive connector cap 45 which has a dished center section 47 fitted in the spring 43, and an outer flange 49 adapted to overlay the outer end of the sleeve 35. The cap 45 is held in place within the body 31 by an insulating plug 51 which is threaded into the body 31. As seen in FIGS. 1 and 2, the plug 51 is exposed at the outer surface of the housing 13 and is slotted at 52 to facilitate removal thereof from the body 31 by means of a screwdriver, without dismantling the housing 13. This in turn facilitates quick and easy brush inspection and/ or replacement.

In use, electric current passes from the lead 39 to the garter spring 41, through the sleeve to the cap and thence to the brush 25 by way of a pig-tail 53 which is fixed at one end to the dished part 47 of the cap 45 While its other end is embedded in the brush 25. The sleeve 35 and the cap 45 are, therefore, electrically live. Thus, it is important that an effective seal be formed between the body 31 and the plug 51 to prevent moisture from entering the body 31 and forming a conductive path from the live parts (i.e. the cap 45 and sleeve 35) to the grounded metal housing 13. In the past, this seal has been formed using flexible washers or O-rings; however, these extra parts can be lost or misplaced particularly when the plug is removed for brush inspection. Then, when the brush components are reassembled, the washer or O-ring often is left out so that the joint between the body and plug is no longer moisture proof. Thus, moisture can enter the body 31 and cause a shock hazard.

In contrast, the present invention makes use of only the basic brush holder assembly components to form a moisture-proof seal. Thus, no extra parts which can be lost or misplaced, are required and a moisture-proof seal is effectively formed each time the components are assembled.

As seen in FIGS. 2 and 3, the plug 51 is undercut at 56 and is provided with an annular, deflectible ring 58 adjacent its inner end and which, when the plug 51 is fully threaded in the body 31, is positioned to engage an annular surface 55 on the inside of the body 31. The inner end of the plug 51 is conically tapered forming a conical surface 57 which converges in a direction away from the direction of brush travel, or away from the commutator 27. The outer end of the cap flange 49 is also conically shaped and converges in this same direction but at a less inclined angle than the surface 57. The outer end of the sleeve 35 provides a seating surface 59 for the cap 45 and may be conically tapered forming a surface 61 which may be inclined substantially at the same angle as the cap flange 49 or the plug surface 57. Alternatively, the sleeve 35 may be cut away at the area of the inclined surface 61.

When the plug 51 is threaded into the body 31, the undercut ring or lip 58 closely but freely clears the inner surface 55. However, as the plug 51 is tightened into the body 31, the conical surface 57 engages the stiff, relatively stationary flange 49 on the cap 45 and the lip 58 is cammed or deflected radially outwardly into tight, sealing engagement with the body surface 55. The rounded shape of the lip outer surface is flattened as the lip 58 is pressed against the body surface 55 and provides sealing engagement over a relatively large area. Thus, moisture is prevented from gaining access to the body 31 and a shock hazard situation never arises.

By the foregoing, there has been disclosed an improved, moisture-proof, brush holder assembly calculated to fulfill the inventive objects hereinabove set forth, and while a preferred embodiment of the present invention has been illustrated and described in detail, various additions, substitutions, modifications and omissions may be made thereto without departing from the spirit of the invention as encompassed by the'appended claims.

I claim:

1. A moisture-proof brush holder assembly comprising a housing, an insulated brush holder body mounted in the housing, a conductive sleeve within the body, a brush guided for longitudinal sliding movement Within the sleeve, a connector cap having an annular peripheral flange at least a portion of which is seated on said sleeve, 2. spring between the cap and the brush constantly urging the brush out of the sleeve, the annular peripheral flange on the cap being provided with a conically-tapered surface Which converges in a direction away from the direction of brush travel, and an insulated plug threadably engaged with the insulated brush holder body, said plug having an innermost undercut annular portion provided with a conically-tapered surface engaging the respective conical surface of said cap, whereby said annular portion of said plug is cammed radially outwardly into sealing engagement with said body as said plug is tightened therewithin, thereby providing a seal which prevents moisture from entering the brush holder assembly and otherwise creating a shock hazard.

2. In an electric motor device of the type having a housing with an electric motor supported therein, a moisture-proof brush holder assembly accessible externally of the housing and comprising an insulating body having a pair of ends, brush means having a portion extending through one end of the holder internally of the housing, plug means connected to the other end of the holder and accessible externally of the housing, stationary means within said body, said plug means having a continuous, deflectable portion engageable with said stationary means and cooperable with a complementary continuous surface on said body, whereby said continuous portion is deflected by said stationary means into tight sealing engagement with said body surface when said plug means is connected to said body.

3. A brush holder assembly for use with an electric motor device, said assembly comprising an elongated body having an opening therethrough, a substantially continuous annular surface in said body, a carbon brush slidably disposed in said body, spring means Within said body behind said brush and normally biasing said brush outwardly of one end of said body, stationary cam means in said body, a plug threadedly received in the other end of said body and having a substantially continuous, deflectable annular portion adjacent the inner end of said plug, said annular portion engaging said cam means, whereby to deflect said annular portion into tight sealing engagement with said body surface when said plug is threaded into said body.

4. An assembly as defined in claim 1 wherein the conically tapered surface on the plug is inclined at a greater angle than the tapered surface on the cap.

5. An assembly as defined in claim 1 wherein said plug is exposed and accessible from outside said housing.

6. A brush holder assembly as defined in claim 2 wherein said continuous portion on said plug means is annular and has a conically tapered innermost surface which converges in a direction away from said brush, said annular portion having an outer peripheral surface engageable with an inner annular surface in said body to effect said sealing engagement.

7. A brush holder assembly as defined in claim 6 wherein said stationary means has a conically tapered surface engageable with said conically tapered surface on said annular portion and which is inclined at a lessor angle than said annular portion tapered surface.

8. A brush holder assembly as defined in claim 2 wherein said stationary means is electrically connected to said brush and forms part of the conductive path thereto.

9. An assembly as defined in claim 1 wherein said sleeve has a conically tapered surface facing said cap flanged portion, said sleeve tapered surface being inclined at a greater angle than the tapered surface on the cap.

10. An assembly as defined in claim 3 wherein said stationary cam mean comprises a conductive cap electrically connected to said brush.

11. An assembly as defined in claim 3 wherein said annular portion has a peripheral surface engageable with an inner surface on said body to effect said sealing engagement.

12. An assembly as defined in claim 3 wherein said annular portion has a tapered surface on its innermost end adapted to engage a confronting surface on said stationary cam means during threaded insertion of said plug into said body.

13. An assembly as defined in claim 3 wherein said annular portion has a conically tapered surface which converges in a direction away from said brush, said stationary cam means having a conically tapered surface confronting said plug tapered surface and inclined at a lessor angle than said plug tapered surface.

References Cited UNITED STATES PATENTS MILTON O. HIRSHFIELD, Primary Examiner. GERALD P. TOLIN, Assistant Examiner.

US. Cl. X.R.

U.S. DEPARTMENT OF COMMERCE PATENT OFFICE Washington, 0.6. 20231 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,436,578 April 1, 1969 Richard T. Walter It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, lines 19 and 20, "connector" should read brush line 20, "brush" should read connector Signed and sealed this 21st day of April 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JB

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

